The present invention relates to the field of linear drive trains and, more particularly, to improved traveler and guide rail apparatus for screw drive closure operators, such as garage door operators. Specifically, the present invention is directed toward an improved minimal cost traveler and guide rail apparatus for a garage door operator.
U.S. Pat. No. 3,858,452 discloses a linear drive train for a screw drive closure operator which includes an elongated guide rail having a screw channel and a track formed by oppositely disposed U-shaped channels in proximity to the screw channel. A screw is contained within a liner in the screw channel, and the screw engages a nut which is carried by an inner traveler to propel the inner traveler along the interior of the track which is formed by the U-shaped channels. An outer traveler is configured to slide along the exterior of the U-shaped channels and includes a latch to selectively couple the outer traveler to the inner traveler for cooperative movement along the track.
The guide rail includes a substantial amount of material, such as aluminum, a large portion of which is included in the U-shaped channels which form the track. Due to the high cost of aluminum, it is desirable to reduce the amount of material which forms the track so as to reduce the cost of the linear drive train and thus reduce the cost of the operator.
More importantly, it is also desirable to provide an improved guide rail and traveler apparatus wherein the guide rail requires only a minimum of material, and yet the benefits of a two-part traveler and its operation are retained. The maintenance of a two-part traveler apparatus is particularly important in those operators wherein the control device depends on constant positioning of an operative traveler with respect to the screw. For example, such an operator, as is well known, may include a control device having switch actuating control cams driven up and down a positioning lead screw in the control device. A traveler constantly connected to the elongated drive screw is thus required, for, if disconnected, the traveler's position on the screw would be out of register with respect to the position of the control cams. A two-part traveler apparatus, wherein one traveler is constantly connected to the screw is highly desirable and useful.